Stabilization of alkyl phenol



Re. 24,834 Reiesued June 7, 1960 STABILIZATION OF ALKYL PHENOL COMPOUNDS aeob J. Menn, Suflfern, N.Y., and Edwin G. Wallace, Walnut Creek, Califl, assignors to Shell Development Company, Emeryville, Calit'., a corporation of Delawere No Drawing. Original No. 2,727,928, dated Dec. 20, 1955, Ser. No. 400,109, Dec. 23, 1953. Application for reissue Mar. 4, 1957, Ser. No. 643,900

- 32 Claims. (Cl. 260-624) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention relates to the stabilization of alkyl phenol compounds, it being particularly directed to a process for improving the resistance of said compounds against deterioration in color and odor with age.

The alkyl phenols, wherein at least one of the hydrogen atoms attached to the phenyl nucleus is replaced by an alkyl group, are normally light-colored compounds having a mild odor when freshly prepared. However, many of these compounds take on a definite discoloration when 2 acids; phosphorus acid; hypophosphorus acid; and the polyphosphoric acids such as the polyrneta-phosphoric acids (HPOQ and the polyphosphoric acids of the pyro: phosphoric acid type having the formula H P O In these formulae 2: is at least 2, generally 2 to .6, although other polyphosphoric acids can also be used.

1 Another suitable type of polybasic acid of phosphorus is allowed to stand, at the same time acquiring a strong and rather unpleasant odor. This deterioration in quality is particularly manifest in the case of the polyalkyl phenols, many of which, especially the 2,4,6-trialkyl phenols, are employed as oxidation inhibitors in materials where it is important that there shall be no change in the color or odor of the resulting composition.

It is a general object of the present invention to provide a method for improving the resistanceof alkyl phenols to deterioration in color and odor with age. A further object is to provide a method of this character which may be effectively employed in the treatment of polyalkyl phenols. The compound 2,6ditertiarybutyl-4- methyl phenol, although possessing outstanding inhibitor qualities, is especially susceptible to yellowing and odordevelopment during storage, and it is a particular object to provide a method for improving the colorand odorstability of this compound. The nature of still other objects of the invention will be apparent from a consideration of the descriptive portion to follow.

It has been discovered that the stability of alkyl phenol compounds against deterioration in color and odor can be greatly improved by treating said alkyl phenols with a polyfunctional acid of phosphorus compound, especially the polybasic acids of phosphorus and their salts or esters. As a result of this treatment, it is possible to produce from alkyl phenols, which would otherwise discolor and acquire an unpleasant odor after a short interval, stabilized alkyl phenols which are 'capableof being stored for many months without exhibiting any appreciable change in color or odor.

The polyfunctional acid of phosphorus compound employed in stabilizing the alkyl phenol can be selected from a wide variety of compounds. Representative stabilizer compounds of this type, any one or more of which can be used in the process of the present invention, are, in addition to the previously mentioned preferred polybasic acids of phosphorus and the salts and esters thereof, the monobasic phosphorus acid compounds which contain at least one additional functional group in the molecule, for example, an amino or hydroxyl group or the like. Typical polybasic acids of phosphorus which have been found to be effective in stabilizing alkyl phenols according to the invention are, for example, the phosphoric acids, particularly ortho-, pyroand hypo-phosphoric the primary phosphonic acids represented by the general formula in which R is an organic radical linked to the phosphorus atom by a direct carbon-to-phosphorus bond, examples of such acids being, for instance, methane phosphonic acid, trichloromethane phosphonic acid, 3,5,5-trimethylhexyl phosphonic acid, benzene phosphonic acid, etc. Other suitable polybasic organic acids of phosphorus can also be used, it being preferable as a general rule to employ those which contain from 1 to about 12 carbon atoms per molecule.

Especially suitable salts of acid of phosphorus compounds are the alkali metal and ammonium salts, for example, mono-, diand tri-ammonium, sodium, potassium and lithium phosphates, phosphites and polyphosphates. The alkali metal and ammonium ortho-phosphates have the advantage of being cheap, readily available and less corrosive than the free acid which, however, is somewhat more effective. Salts of polyphosphoric acids which are suitable stabilizer compounds are readily prepared, for example, by fusing mixtures of orthophosphoric acidsalts with bases or by fusing mixtures of salts of monophosphoric acids and polyphosphoric acids. In this way a large number of different polyphosphoric acid compounds can be produced, each differing only slightly from its adjacent members of the series and all being eifective in the process of the invention. Mixed salts as well as simple salts can be used, and with the polybasic polyphosphoric acids of high molecular weights the mixed salts having both monovalent and polyvalent anions are particularly suitable. Thus, mixed salts having alkaline earth metal or aluminum or zinc ions together with alkali metal ions, for example, the calcium-sodium or magnesium-potassium or aluminum-ammonium salts of high polyphosphoric acids, can be used advantageously. With such salts it is preferred that the ratio of monoyalent anions to polyvalent anions present be high, as the water solubility is thereby improved. Representative examples of other suitable polyphosphoric acid salts are, for instance, sodium trimetaphosphate (NaPO sodium tetrametaphosphate (NaPO,) sodium hexametaphosphate (NaPO tetrasotlium pyrophosphate disodium dihydrogen pyrophosphate NEtgH PgOq, trisodium hydrogen pyrophosphate N33HPg07, sodium tetraphosphate Na P o the complex fusion product from two moles of monosodium dihydrogen phosphate and one mole of disodium monohydrogen phosphate Na P O Thiopolyphosphates may be used in place of or in con junction with the foregoing salts. Examples of salts of this type which are useful are, for instance, sodium monothiotetraphosphate Na P O S and sodium trithiotetraphosphate Na P 0 S These compounds have the same general efiiciency as the other Water-soluble polyphosphoric acid compounds in improving the color and odor stability of alkyl phenols according to the invention.

Instead of the foregoing inorganic salts, amine salts of acid of phosphorus compounds can be effectively used,

as the stabilizing agent. Aliphatic, aromatic and alicyclic 3 amines which can be primary, secondary or tertiary are suitable. 'Salts of acids ofphosphorus'and amines having 1 to 12 carbon atoms per molecule are generally preferred. Methyl, ethyl, isopropyl, tertiary butyl, cycle? hexyl, phenyl and like amine salts of ortho phosphoric,

' tetraphosphoric and hexameta phosphoric acids, for exphor'icac'id esrers'or water-s 1 bleinonoi, s

alcohols such as ethyl, iso rs l 7 1161s. glycerol, glycol, pentasg tol, n y a ohols, and t e k T e rq yc a s h r s a'd, e.g. the pyrophosphoric and tetraphosphor' ers are equally suitableC Aniino-s ari e'specially advantageous subgroup esters usetul in the new process. Esters of polyhydric alcohols or aminosiibs'titutedalcohols are the preferred meta-phosphoric acid esters. Thus, glycerol monometaphosphate, betaarninoethyl metaphosphate, ethylene glycol dimetaphosphate and the like are suitable. i

Another type of esters which are suitable is the phosphates of aliphatic esters of amino acids. US Patent 2,103,558 describes a number of useful esters of this type prepared from orthophosphoric acid and esters of amino acids such as glycerol and sarcosin' and having the gen-. eral formula (NX R'COQR)H PO wherein X is hydro: gen or a substituent element or group, e.g. alkyharninoalkyl, imidoallcyl, chloroalkyl, hydroxy-alkyl or the like, and R and R represent alkyl, aryl, aralkyl, alicyclic or heterocyclic alkyl radicals. Addition products of meth-. yl, ethyl, isopropyl, tertiary butyl and like esters of tyre:

sine, tryptop hane, and creatine with orthophosphoric acid. are typical useful compounds of this class which can be used in stabilizing according to the present invention. However, the corresponding products from metaphos-. phoric acid and the various polyphosphoric acids and, their acid salts such, for instance, as mono-sodium dihydrogen'pyrophosphate and thelike, are. equally. useful in thc new process.

Whatever the type of, polyfunctional acidofiphosphorus compound chosen as the. stabilizer compound, it should be one which is soluble inthetreatingmedium under the conditions of its application to. the'alkyl phen'ol being stabilized to an extent. sufficient to form a solution co'n compound-based upon the alkyl phenol present.

The process of the present invention can be practiced with good effect in the case of any alkyl phenol. It is especially advantageous with alkyl phenolshaving an alkyl group of 2 to carbon atomsin the molecule. Representative starting compounds ofthis type are the Yarrouscresols, 0-, m and p-ethyl'ph'enol, p-prop yl 'phe nol, p-isopropylphenol, p-tertiaryltiutyl phenol, 2 ,4 di"- tilillifig at least 0.01% by weight ofi-such polyfunctionah Q 4 r tained in the treatment and resultant stabilization of th polyalkyl phenols, many of which are given above. These polyalkyl phenols are prepared by conventional processes, the usual method being to heat phenol or an alkylated phenol derivative such as o-, mor p-cresol with an alkeue i the Es enc of n acidic condens ng agent such as sulfuric acid, phosphoric acid, hydrogen chloride or ferric chloride, the alkene attaching to one or more at .th or atom o th henylnucleus, depen ng on the reactant proportions employed. The next step in the process is usually to neutralize the reaction mixture with aqueous caustic solution, following which the neutralizedp oduct iswashed and, if desired, further purifled, asliv talli it s e. product o or m t m from an alcoholic or other liquid solution. The products so obtained are normally light in color and possess little objectionable odor although many darken rapidly and e o n 0 21' ca e odo as th y a e stored.

"maul Ph nol c mpound are stabilize jby eatment withan acid of phosphorus or salt thereof in the presence of a solvent for the stabilizer or for both the stabilizer and the alkyl phenol. When present in the molten condition, the alkyl phenol can itself act as the solvent, although other solvent media such as water, ethyl, methyl, isopropyl and various other alcohols, as well as ethers such as diethyl ether, methyl ether of diethylene glycol and the like, can be used. Thus, the stabilizer compound, in either the presence or absence of a solvent, can beadded to a system wherein the alkyl phenol is present in the liquid condition. Again, a solution of the acid or salt can be added to the solidalhyl phenol compound. The details of several available treating methods will be set forth'in the examples.

The amount of the stabilizingagent to be employed is susceptible to some variation. Thus, amounts as small: as 0.01% of the acid orsalt, in terms of the weight'of alkyl phenol compound present, have given good results, although-preferably there is employed at least 0.05% of the stabilizing additive. Again, good results have been obtained using amounts thereofasla-rge as 5%, although for reasons of economyit seldom paysto use more than about 1% since any additional benefits so gained do not justify-the added expenditure.

Particularly when using asthe stabilizer compound an acid of phosphorus com-pound which is strongly acidic, it isdesirable to control the conditions of treatment so as to avoid conversion ofthe alkyl phenol being Stabi lized; "I hus, in such cases it is; generally desirable'to carryout the treatmentv at a temperature below about 125 C. in order to avoid any appreciable dealkylation of the allcyl phenol. Excessively long periods of treatment atthe higher permis-sibletemperatures are also preferably avoided, treatment times of not substantially more than 3 hours being prefer-red. When employing salts ofi acids of phosphorus, especially the preferred mono-and: ii-alkali metal and ammonium salts of phosphoric acid, or esters of phosphorus acids, higher temperatures and longer treating times can be used without methyl phenol, Z-methyl-ttertiarybutyl phenol, Z-tertiarybutyl-4-methyl phenol, 2-methyl-4 dodecyl phenol, 2,4-drtertiarybutyl phenol, 2,6-diethyl phenol, 2-methyl-, 6-tert1arybutyl phenol, 2,4,6 trimethyl phenol, 2 ,6 -di-. ethyl-4-methyl phenol, 2,4,6 triethyl phenol, 2. 6-dipropyl-4-methyl phenol, 2,4, 6,-tripr'opy1 phenol, 2, 6-diethyl- 4-tertiarybutyl phenol, 2-tertiarybutyl 46 A "i 01, 2,4,6-tritertiarybutyl phenol, 24 nol, 2,4,6-tritertiaryamyl phenol, H tertiaryamyl phenol, 2 tertiaryarnyl-4,6-dimethyl ph ol, 2 -isopropyl-4,6-dimethyl v amyl phenol'and 2,6-ditertiarybutyl-4-tertiaryamy1 phenolr However, particularly'good resuIts ha e been ob sti onil plie dimethyl phe-.

phenol, 4-methyl-2, 6-ditertiary danger-ofconversion of the starting alkyl phenol; .As a general rule, temperatures of about 0" C. to about" C. and treatment times of about 2 minutes to 3' hours, preferably about 10' to 60 minutes, are advantageous when using either the freeacids or the salts as stabilizer compounds.

It is a feature of'the present invention that the stabilizing-action exerted" by the added acid orsalt compound employed persists eventhough the stabilized alkyl phe-. nol compound is thereafter given one or more of various washing or' even recrystallization treatments with solent h h m ther s be expectedv to emo e, ny o he ci alt lizer pre enthis sm d a ags sin e h t bil et. e a ded t he alkrlph nel wmpollnd. t the con en nce if t e opera o j ecd 19? 9. added. d ing. he. in treat si steps- 1. some cases the latter are practiced only after the lapse ofa EXAMPLE I A. A quantity of 2,6-ditertiarybutyl-4-methyl phenol was prepared by alkylating p-cresol with isobutylene in the presence'of a minor amount of concentrated sulfuric acid as catalyst. The acid alkylate produced in this manner was then neutralized with aqueous caustic solution and water-washed. The resulting product was then combined with an equal weight of a solvent made up of 85% isopropyl alcohol and 15% water at 60 C. The resulting solution was then cooled to room temperature, thereby crystallizing out the alkyl phenol. These crystals were recovered, washed with fresh quantities of the isopropanol solvent, and air dried. As indicated in the table which follows Example III, the crystalline product so obtained, which was originally white in appearance, and had a mild odor, became progressively darker as it was allowed to age. At the same time, its original mild odor changed in character and grew progressively more unpleasant.

-B. Companion operations were conducted. under the same conditions as those described in the foregoing paragraph, except that here the neutralized alkylate was washed for a period of 30 minutes not with water, but with a hot (80 C.) 1% aqueous solution of diammonium phosphate, the amount of wash solution employed being such that the quantity of diammonium phosphate stabilizer present amount to 0.3% by weight of the 2,6-ditertiarybuty1-4-methyl phenol. As will be seen from the following table, the crystalline product which had earlier so obtained was twice washed with the alcohol-water solvent,- after which the crystals were air-dried for two days. As indicated by the data present in the table, the crysta1- line product obtained in this manner rapidly deteriorated with age.

In companion operations conducted under otherwise the same conditions as described in the preceding paragraph, diammonium phosphate and sodium tetraphosphate (Na lflo were introduced along with the alcoholwater solvent media from which the product was crystallized. As shown in the table, each of these additives effectively stabilized the product against deterioration in color for the 18 weeks during which they were tested. In contrast with the product which had been similarly treated Without these additives, there was no deterioration in either color or odor of the thus stabilized alkyl phenol.

EXAMPLE III A mixture of caustic-neutralized 2,6-ditertiarybutyl-4- methyl phenol (1000 parts), isopropyl alcohol-water azeotrope (200 parts) and orthophosphoric acid (2.5 parts) was stirred vigorously at 80 C. for 30 minutes. The organic layer was separated by decantation and the trialkyl phenol was crystallized therefrom by cooling to ambient temperature with moderate stirring. The crystals were recovered by vacuum filtration and washed once with 100- part and twice with -part portions of isopropyl alcohol-water azeotrope. After drying at room temperature for four days, the crystals were stored in the dark. After 35 weeks of storage, the crystals were essentially unchanged in either color or odor. determined on the melted crystals, was less than one. Equally good results are obtained when tetraphosphoric acid is used in place of the orthophosphoric acid, but crystals from the same plant alkylation batch which were similarly treated without addition of a stabilizer deteriorated noticeably in color and odor in three weeks.

Table STABILITY OF 2,6-DITERTIARYBU'IYL-i-METHYL PHENOL Gardner Color No. 0! Melt After Storage for Wt. Per- Example Stabilizer cent No. Stabll- 0 2 4 B 14 18 izer 1 weeks weeks weeks weeks weeks weeks I-A N 1 5 12 13 I-B Diammonium 0.3 1 l 1 2 phosphate. IT None 1 2 4 6 8 8 II Diammonlum 0.3 1 1 1 1 1 2 phosphate. II Hexasodium 0.3 1 1 2 2 2 2 tetraphosphate. III None 1 2 4 8 9 9 III Phosphoric 0.26 1 1 1 1 1 1 acid (H P0 1 Based on the 2,G-ditertiarybutyl-i-methyl phenol present. 1 0n the Gardner Color Scale, No. 1 corresponds to a nearly water-white 1i uid. N o. 5

is a very pale yellow, and No. 10 is a deep yellow.

This scale is defined in t e reference work by Gardner and Swsrd, Physical and Chemical Examination, Paints, varnishes,

Lacquers, Colors, 4723 Elm St, Bethesda,

been washed with the diammonium phosphate solution was little changed in color during the storage period. Its odor was also unchanged during this period.

EXAMPLE II liquid being maintained at 80 C. for one-half hour. At

'the end of this period the organic layer was separated .and then cooled, with stirring, to room temperature to 1950 215 page 9. Published by Henry A. Gardner Laboratory, Inc.,

EXAMPLE IV In this operation fresh crystals of 2,6-ditertiary butyl- I 4-methyl phenol prepared in the manner described in Example I, paragraph A, are slurried at room temperature with one-third their weight of a 1% solution of trisodium phosphate in a solvent made up of isopropyl alcohol and 15% water for about 30 minutes. The treated crystals, after recovery and drying as described in Example III, are stable in color and odor during long storage in which the untreated crystals become badly discolored an develop a strong unpleasant odor.

EXAMPLE V In this operation untreated crystals, prepared as de- -crysta1lize out the alkyl phenol. The crystalline product 7 6 scribed in Example I, paragraph A, are placed on a Buch- Their Gardner color,'

net funnel and washed at room-temperature with one- EXAMPLE VI In plant scale tests of the process, .diammonium phosphate was used to treat the product of a1kylating paracresol with isobutylene in the presence :of sulfuric .acid. In one case, ten pounds of .diammonium phosphate were added to 125 gallons of Water'used to tank-wash about 3000 pounds of neutralized alkylate and the phases were mixed'by pump circulation for one hour-at 85 C., after which the lower aqueous phase and the 'alkylate were recovered, crystallized and dried. In theother case, diammonium phosphate in an amount of 01.15% by weight, based on the alkylate, was added to the crystallizer in the form of a 35% aqueous solution, and the mixture stirred at 65 C. for one hour, after which the crystals were recovered and dried in the same way. Both prod ucts were completely stabilizedand had a Gardner color for the melt of 1 after 12 weeks" storage, during which time there was no deterioration in odor.

Similar good results are obtained when sodium phosphite is substituted for the ammonium phosphate in these operations.

It will thus he scen that the process can be successfully carried out with a wide variety of acids of phosphorus and salts thereof, and it will be understood that the invention is not limited to the examples which have been given by way of illustration since any alkyl phenol having an alkyl group of at least two carbon atoms can be efiectively stabilizedwith anyofthese stabilizer compounds.

This application is a continuation-in-part of our copending application, Serial No. 239,184, filed July '28, 1951, now U.S.Patent 2,672,485, issued March 16, 19-54.

We claim as our invention:

1. The method for improving the colorand odorstability of an allcyl phenol which tends to become discolored and to develop an odor with age which comprises treating said alkyl phenol with 0.01% to .based on the weight of alkyl phenol, of polyfunctional .acid of phosphorus compound at a temperature below 125 C. for .a period between about 2 minutes and 3 hours .at which no substantial conversion of said alkyl phenol takes place and recovering the starting .alkyl phenol :as stabilized product.

2. The method of claim 1 wherein the treatment is :oarried-out in1the presence :of aliquid solvent for-said polyfunctional acid of phosphorus compound.

3. The method for improving the colorand odorstability of an alkyl phenol comprising washing said alkyl phenol with :an aqueous alcohol solution of at least one polyfunctional .acid of phosphorus compound at a temperaturebelow 125 C., the amount .of said phosphorus compound being 0.01% to 5% by weight of said alkyl phenol, and recovering the starting alkyl phenol as stabilized product.

4. The method for improving the colorand odorstability .of an .alkyl phenol comprising crystallizing said alkyl phenol from a solution containing 0.01% to about 1%, based on the weight of alkyl phenol present, of polyfunctional .acid of phosphorus compound at a temperature below 125 .C., the amount of said phosphorus compound .being 0.01% to 5% by Weight of said alkyl .phenol, and recovering the starting alkyl phenol as stabilized product.

5. The method .for improving the .colorand odorstability of 2,6-ditertiarybutyl-4 methyl phenol comprising treating said alkyl phenol with at least one polyfunctional acid of phosphorus compound at a temperature below 125 -C., the amount of said'phosphorus compound 0.01% to "5% by"weight of :said -alkyl phenol, and

recovering the '2;6-ditertiarybutyl-4-methyl phenol as stabilized product.

6. The method of claim 5 wherein the polyfun'ctiona'l acid of phosphorus compound is phosphoric acid.

7. In the alkylation of a phenol by reaction with an alkylating agent in the presence of a catalyst, the method for improving the colorand odor-stability of the alkylated phenol which comprises separating the alkylated phenol from the alkylation mixture and contacting it with 0.01% to 5% by weight of a polybasic acid of phosphorus compound at a temperature of about 0 C. to C. 'for a time between about 2 minutes and 3 hours at which no substantial conversion of said alkyl phenol takes place and recovering the starting alkyl phenol as stabilized product.

is. The method of claim ,7 wherein-theallgyletedp fino is stabilized by treating .it with 0.01% toabout 1% ,by v1v(t)=.'(ijghJ of orthophosphoric acid at about 20 ..C. .to about 9. The method of claim8 herein the alkylated ph nol is a P ct of alkylation of a me hy 'phenol with an olefin of 3 to20 carbon atoms in the presence of sulfuric acid as catalyst.

10. In the alkylation ofparacresol by reaction with an isobutylating agent .in the presence vof .jan alkylation catalyst wherein 2,6-ditertiarybutyl-4-methyl phenol .is produced, the method for improving the colorand odorstability of the 2,6-ditertiarybutyl-4-methyl phenol which comprises separating the .2,6+ditertiarybutyl-4-methyl phenol from .the alkylation ,mixture andcontacting it .for not substantially more than 3 ,hours with0.01% :to-5% by weight of a polybasic acid of phosphorus compound at a temperature .of about.0 C. to 125 C.

.11. The method for improving the colorand OdOrstability of anial-kyl phenol comprising treatingsaid a1kyl phenol with 0.01% to 5%, based on the weight .of .alkyl phenol, of a polybasic phosphoric acid salt.

12. The method for improving the colorand odorstability of an alkyl phenol comprising treating said alkyl phenol with 0.01% to 5%, based on the weight of alkyl phenol, of an alkali metal phosphate.

13. The method of claim 12 wherein the alkali metal phosphate is hexasodium tetraphosphate.

14. The method for improving the colorand odorstability of an alkyl phenol comprising treating said alkyl phenolwith 0.01% to 5%, based on the weight of alkyl phenol, of an ammonium salt of a polybasic phosphoric acid ammonium salt.

15. The method of claim 14 wherein the ammonium salt is diammonium phosphate.

16. The method for improving the colorand odorstability of an alkyl phenol comprising treating said alkyl phenol with 0.01% to 5% based on the weight of alkyl phenol, of a polybasic phosphoric acid salt of an amine having ,1 to 12 carbon atoms per molecule.

17. The method for improving the colorand odorstability of an alkyl phenol comprising treating said alkyl phenol with an ester of an acid of phosphorus having 1 to 20 carbon atoms per molecule, present in an amopnt equal to 10.01% to 5% by weight ofsaid alkyl phenol.

18. The method of claim 17 wherein the ester is a hydroxy phosphate.

19. The method of claim 17-wherein the alkyl phenol is ,2,6-ditertiarybutyl-4-methyl phenol.

20. Crystalline alkyl phenol vcontaining an effective amount notg reater than 0.1% by weightjof a polyfizmctiona'l acid ofphosphorus compound as stabilizer against development of oolorandodor during storage.

21. Crystalline alkyl phenol containing an efie ctiue amount not greater than 0.1% by .weight ofra Phosphoric acid as stabilizer against aevelopmentof c0lorand ,odor during storage.

22. An a'lky'l substituted phenol containing between about 0.1% and 0.01% by weight of a phosphoric acid as an inhibitor of color darkening on storage.

23. An alkyl phenol containing an efiective amount not greater than 1% by weight of a non-acid polyfunctional acid of phosphorus compound as stabilizer against development of color and odor during storage.

24. An alkyl phenol containing an efiective amount not greater than 5% by weight of an inorganic salt of a polybasic acid of phosphorus as stabilizer against development of color and odor during storage.

25. Crystalline alkyl phenol having at least four carbon atoms in the alkyl group containing betweenabout 0.01% and 0.1% by weight of a polyfunctional acid of phosphorus compound.

26. 2,6-ditertiary-butyl-4-methylphenol in admixture with between about 0.1 and 0.01% by weight of a phosphoric acid.

27. Para-tertiary-butyl phenol in admixture with between about 0.1 and 0.01% by weight of ortho-phosphoric acid.

28. Method of inhibiting discoloration of an alkyl phenol on storage in a molten condition, which comprises incorporating in the alkyl ph enol between about 0.1% and 0.01% by weight thereof of a phosphoric acid.

29. An alkyl substituted phenol containing between 10 about 0.1 and about 0.05% by weight of a phosphoric References Cited in the file of this patent or the origmal patent UNITED STATES PATENTS 2,223,549 Harvey Dec. 3, 1940 2,383,279 Stillson et a1. Aug. 21, 1945 2,559,594 Caplan July 10, 1951 2,752,398 Riley June 26, 1956 OTHER REFERENCES Hart et :al.: J'our. Organic Chem, v01. 15 (March 1950), pages 396-9 (4 pages). 

